Advice on diaphragm, jet needle, and float height.

[lewkmiller]

Hello. I have read a lot of information on float height and I am thoroughly confused. I have a 1978 xs400 2E (looked up VIN) and my first project was to go through the carbs. The guy I bought it from said it needed new "points and jets" I have gone through the carbs and they look great. One has more build up than the other which was odd. I have a picture below of the jet needles and was looking for opinions on if they need to be replaced. I also am wondering if the diaphragms need replacing? Does anyone have a good method of soaking carbs? I have heard vinegar? Also I need some input on where to set my floats at? Thanks people! Viva el XS!!

 

[xschris]

http://www.xs400.com/forum/showthread.php?t=12330 He has a good video on how to clean carbs.

 

[lewkmiller]

xschris, thanks! I was watching his low res version and had no idea he made a new HD one. This is great! Thanks for the link.

 

[Wolfe_11B]

Hold the diaphragms up to a light and see if they have any pin holes or soft spots. I'd replace them with a set of these anyway, they are much nicer than the Yamaha ones- http://jbmindustries.com/Yamaha650.html

 

[lewkmiller]

Guys, Thanks for all the info and advice. I got the carbs rebuilt and installed. It started right up! tuned the mix needles and sync. never heard it run so good. one thing though. it is popping every once in a while. ideas?

 

[willem]

sounds like it's running a bit lean. Adjust your idle mixture screws. If that doesn't do the trick check for vacuum leaks, holes in your exhaust, the air filter for damage/wear, set your float height, set idle mixture again, and see what happens

 

[lewkmiller]

So.........with the idle mixture screws, which way does what? I am assuming that the more you tighten/screw them in the more lean, and the more you let them out/loosen them the more rich. Yes? No?

 

[16VGTIDave]

Yes. The Pilot screws are "Idle Mixture" screws on these carbs. On some other carbs they are just air screws.

 

[xschris]

If you need to go out more than four turns you will need to go up on the pilot jets.

 

[lewkmiller]

xschris: I rebuilt carbs and added mikes xs pod filters. I have a 2 into 1 exhaust with standard megaphone. should I get new jets? if so what size do you suggest? also can you recommend a fuel mix needle that will fit my 1978 xs400 2e? Ive looked for these im just never sure which ones to buy.

 

[xschris]

I would go up one on the pilots and 2 on mains. Needle jets for these bike are gone and can't be purchased anywhere that I know of. You can try yamaha for idle mix screws they still had them not to long ago. The member BCWARE runs that setup on his 78 2-E so he should know more about it.

 

[Scorpio1963]

Anytime you make changes to the air flow into your carbs and exhaust jetting is usualy always needed.Id start with going up 2 sizes on the mains and up a size on the pilot.
I had to bump my pilots up 2 sizes to get the carbs tuned.I also dont have turn the mixture screws out as far 2 1/4 turns and 2 1/2 on the other.the bike was running great until this spring when a electrical virus hit it.

 

[lewkmiller]

Ok. Thanks xschris and scorpio. Now how do I determine what size im at now and how to find 2 sizes up jets?

 

[xschris]

Yamaha will have jets. My local dealer has the good real mikuni jets ( I would recommend) or the Chinese knock offs that mikesxs sells.

 

[Scorpio1963]

I bought my pilot jets from one of the local bike shops in my area,as for my mains I have a micro size drill bit set.I drilled my mains and up the size.I dont recogmend this unless you know what your doing.You can easily mess up the hole inside the mains.
the mains and pilot jets for mukini carbs are easy to find.

 

[lewkmiller]

Ok... so.... I went to my local yamaha dealer and got jets! I bought 2 steps up from stock and 3 steps up from stock for main jet. 1 and 2 steps for pilot. I got home and started my bike jus to try to work with current jets. I got it started and it ran great.... on full choke. as soon as i closed choke down it died. i have fuel mix needles 2 turns out. is this indication I need bigger jets?

 

[Edgee2004]

Did the engine warm up before you turn the choke off.

 

[lewkmiller]

No. I was going to try to push choke in but it died. I think I have a battery charging problem as well. Gotta fix that one first I think.

 

[Edgee2004]

Let it warm up first.

Put a voltmeter across the battery. 14v?